USE OF WATER BY SPPJXG WHEAT OX GREAT PLAIXS. 
29 
Comparison of Figure 10 with Figure 9 shows some interesting 
facts. In the first place, the quantity of water calculated as neces- 
sary before a yield aboye zero would 'be produced is lower at Xorth 
Platte than at Edgeley in spite of the fact that it is located much 
farther south. The reason for this is not known, unless it is because 
of the shallowness of the Edgeley soil, which makes eyen a short 
drought seriously reduce the yield. 
The point most in eyidence is this : Each bushel of yield at Edgeley 
requires 0.2 inch of water aboye the minimum, and each bushel yield 
at Xorth Platte requires 0.4 inch of water aboye the minimurn. A 
greater mass of data to work from would undoubtedly change the 
20 
/s 
/e 
3 
e 
2 
__ o° I ^ 
^^>-^ i"l : I i I I ~ 
I I I I n i I ' \ — 
'. \ ; I 
/O /2 /^ /6 /e 20 22 24 2S 23 30 <32 3^ 36 
^^^•i l?-~^^^^^?^ showing the yield of wheat and use of water on plat A at North 
^r J- oo n^;x ^'^^ ^^ years. The line is drawn from the linear-regression equation 
slope of these lines somewhat, but it is apparent that the quantity of 
wat€r necessary to produce each successiye bushel of yield is much 
higher at Xorth Platte than at Edgeley. 
The linear-regression formula has been used in computing yields 
at Xorth Platte. Table 6 giyes for plat A at Xorth Platte the water 
use m inches, the actual yield, and the ^deld computed by the linear- 
regression equation. 
Table Q.— Actual and computed yields of wheat per acre on plat A at North 
Platte, Xehr., in the nine years stated. 
[The quantity of water used during the growing season as stated in the table forms the 
40^ 1 <^*o°^Puted yield as calculated by the linear-regression equation M=6.22 -i- 
Year. 
Water 
used. 
I Inches. 
1908 14.70 
1909 16.80 
1910 7.75 
1912 9.06 
1914 9.17 
Yield. 
Actual. 
Bushelg. 
22.7 
23.0 
6.8 
12.8 
6.0 
Com- 
puted. 
BtLsJiels. 
21.2 
26.5 
3.8 
7.1 
7.4 
Year. 
Yield. 
Water 
used. 
I Inches. 
1915 ' 16.46 
1916 1 9.98 
1917 1 9.70 
1919 j 14.22 
Actual. 
Busltds. 
•22.1 
17.2 
4.2 
15. 5 
Com- 
puted. 
Bushels. 
25.6 
9.4 
8.7 
20.0 
